Abstract: The forming time necessary to superplastically form an object from a metal sheet is estimated by empirical analysis. The required rate of gas mass flow into a forming cavity is then determined using either a nomograph composed of four interrelated graphs, or a single graph which requires the input of fewer variables than the nomograph. The present invention may also be used to form cells of multiple sheet panels from a stack of sheets. In the latter application, forming time necessary to complete forming of the cells from an interim point where the core sheet forming pressure and the die temperature are increased from interim levels to their final values is estimated by empirical analysis. A nomograph or single graph of the present invention then determines the gas mass flow rate necessary to safely and efficiently complete forming of the cells from the foregoing interim point.

Abstract: An airfoil-shaped structure having a continuous, seamless, structurally reinforced, leading edge is fabricated using a superplastic forming/diffusion bonding process which results in a simpler and more cost effective structure. The airfoil-shaped structure includes a core assembly having welded together core sheets and a facial component being defined by a face sheet having a 180.degree. bend therein so that the two face sheet ends are aligned. To fabricate the airfoil-shaped structure the core assembly is inserted inside the facial component, thereby forming an intermediate assembly having a plurality of cells. The intermediate assembly is inserted into a die cavity, after which the airfoil-shaped structure, having predetermined design characteristics, is superplastically formed by heating the die and selectively pressurizing the plurality of cells using only two forming pressures.

Abstract: A two-sheet superplastically formed/diffusion bonded panel is made with a forming die assembly in which forming cavities are held in a flexible retaining sheet that floats in a forming box. A gas passage is provided through the box behind the cavities and the retaining sheet so that the cavities and retaining sheet are forced toward a rigid face sheet forming die element when pressurized gas is introduced. A face sheet and a reinforcing sheet sealed together around their edges, except for a gas passage to provide pressurized gas between the two sheets, are placed between the face sheet die and the forming die elements positioned in the box. The sheets are then heated and pressurized gas is applied between the sheets to cause the face sheet to move into contact with the face sheet die element while the reinforcing sheet superplastically deforms into the cavities supported by the retaining sheet to form ribs.

Abstract: The method of forming SPF/DB structures having reinforcement webs that are constructed by welding two or more sheets together along an interrupted seam and placing the core so formed between two face sheets, expanding the face sheets into a die by providing pressurized inert gas through one of the face sheets and through a pressure equalization hole drilled through a sealed area formed by the seam, and using pressurized inert gas to expand the core sheets into webs that extend between the face sheets.

Abstract: A method of determining the progress of a superplastic formation process that uses controlled gas-mass flow rate of inert gas to form a part from generally one or more sheets of superplastically formable material, a process that may include selective diffusion bonding of the sheets together. The method includes using the expected initial conditions of the process to calculate a family of constant volume curves plotted on a graph of pressure versus cumulative gas-mass and then comparing the actual pressure and cumulative gas-mass that occurs during the process to determine the health of the process and to determine when the process has successfully completed. The comparison may be performed manually or automatically with a computer which has been programmed to characteristic and non-characteristic progress curve portions.

Abstract: A method to increase the damage resistance of a diffusion bonded panel that includes embedding reinforcing members in the panel are bonding the reinforcing members so structural redundancy occurs adjacent the bonds and the structures constructed thereby. The reinforcing members stop cracking of the panel there across by taking on the load at the end of the crack so crack growth is retarded.

Abstract: Sheet materials are superplastically formed and optionally diffusion bonded into structures, by directly electrically resistance heating the sheets and forming them with a controlled gas-mass flow while the dies in which they are formed may remain relatively cool. The dies include electrodes and thermocouples placed therein, and gas interface ports that connect to the sheets to be formed to allow rapid formation of structures. Some of the gas interface ports may become sealably attached to the part during the formation process so that the structures may be removed from the dies hot, thus allowing a high die throughput.

Abstract: Four sheet SPF/DB panels having thick perpendicular webs formed between face sheets for areas of high compressive stress while other areas have relatively thinner webs so that the overall weight of the panel is not excessive. The thick webs are constructed by welding doubler strips or grids to core sheets when the core sheets are welded together into a core assembly prior to panel formation. When the core assembly so formed is superplastically deformed, the outer edges of the doubler strips bond to the face sheet and then are stretched into the centers of the thick webs, thereby thickening them for additional compressive strength. Normally such are used to reinforce edge joints between panels or supporting structure.

Abstract: SPF/DB structures having diagonal reinforcement webs and processes for the formation of the structures allow greater vertical web height to spacing to be formed. The diagonal webs are constructed by adding at least two additional sheets in the center of a prior art four sheet SPF/DB process. The additional sheets are welded to sheets that will become vertical webs centrally between the webs. When the core assembly so formed is superplastically deformed, the additional sheets are stretched into diagonal webs, which may be longitudinal, lateral, at an angle, or a combination to form truncated pyramidal reinforcements contained in rectangular cells, truncated hexagonal reinforcements of hexagonal cells or diagonally reinforced rows.

Abstract: An improved die for a superplastic formation process and the process that uses an interface for pressurized gas that is part of the forming die so that tube welding to the forming pack can be eliminated. In one embodiment, the interface is fixed to the die and in a second, for use to pressurize the interior volume of finished parts with inert gas when the finished parts are to be removed from the die hot (1400.degree. F.), the interface becomes welded to the pack during the forming process so that the interior of the part can be flooded with inert gas during the cool down process.

Abstract: A method and apparatus for determining the progress of a superplastic formation process that uses cumulative gas-mass outflow from a forming part being formed from generally one or more sheets of superplastically formable material, a process that may include selective diffusion bonding of the sheets together. The method includes using the expected initial conditions of the process to determine the gas-mass cumulative exhaust at room temperature and pressure. The method is advantageous over inlet measuring methods where high pressure gas must be measured and any small hole in the system results in large errors.

Abstract: A perforated sheet is diffusion bonded to a thin solid sheet. Each of the perforations of the perforated sheet is tapered, having a maximum diameter at the surface that is not bonded to the thin sheet and a smaller diameter at the surface that is bonded to the thin sheet. The bonded perforated sheet and thin sheet are included with other solid metallic sheets in a forming pack to be superplastically deformed into a structure. The bonded perforated sheet and thin sheet are placed on the top of the forming pack so that the thin sheet will face outwards after the structure is formed. After the superplastic deformation process is completed, the thin sheet is removed by machining to expose the perforated sheet and provide a structure for controlling laminar flow over the perforated sheet. The exposed surface of the perforated sheet includes the smaller diameter of each tapered perforation, while the inner-facing or blind surface of the sheet includes the maximum diameter.

Abstract: A perforated sheet is diffusion bonded to a thin solid sheet. Each of the perforations of the perforated sheet is tapered, having a maximum diameter at the surface that is not bonded to the thin sheet and a smaller diameter at the surface that is bonded to the thin sheet. The bonded perforated sheet and thin sheet are included with other solid metallic sheets in a forming pack to be superplastically deformed into a structure. The bonded perforated sheet and thin sheet are placed on the top of the forming pack so that the thin sheet will face outwards after the structure is formed. After the superplastic deformation process is completed, the thin sheet is removed by machining to expose the perforated sheet and provide a structure for controlling laminar flow over the perforated sheet. The exposed surface of the perforated sheet includes the smaller diameter of each tapered perforation, while the inner-facing or blind surface of the sheet includes the maximum diameter.

Abstract: The structure and process for making a metallic panel structure from a plurality, e.g. two, core elements each comprised of a pair of sheets of superplastic material welded together along a plurality of weld lines, the weld lines of one core element being spaced differently or of different shape from the weld lines of the other core element. The core elements are joined together, with the weld lines of one core panel positioned at an angle, e.g., normal, to the weld lines of the adjacent core element. The resulting panel assembly is placed in a die. The die is heated to superplastic forming temperature, and gas pressure is applied to the spaces between the sheets of the respective core elements, causing superplastic forming and expansion of the sheets of each core panel to form a first series of bulges between weld lines of one core element, and a second series of bulges dissimilar in shape, e.g.

Abstract: A forming die which includes a die cavity contains a forming blank composed of a metallic alloy having superplastic properties. The forming pressure in a pressurized space adjacent the forming blank is regulated by a pressure regulator. The volume of the die cavity is determined, as is the mass of gas initially contained in the die cavity at the beginning of the forming cycle. The total forming time is empirically determined. The average gas mass flow rate that will be exhausted from the die cavity is calculated by dividing the total mass of gas initially contained in the die cavity by the total forming time. A gas mass flow meter fluidly communicates with the die cavity and measures the mass flow rate of the gas displaced by the forming blank and exhausted from the die cavity. The gas mass flow meter is continuously monitored during the forming cycle or a gas mass flow rate signal is fed back to the pressure regulator.

Abstract: A process for forming single piece metal alloy panel structures includes both superplastic forming and braze bonding steps, and is particularly adapted to superplastically formable materials which are not particularly diffusion bondable, such as aluminum alloys. The process involves constructing a worksheet assembly from a plurality of worksheets which are associated with a brazing alloy capable of brazing the worksheets. At least two of the worksheets are joined in facing contact with each other by welding in a preselected pattern. The perimeter of the joined worksheets is then sealed, with the provision of means for permitting the admission of pressurized gas therebetween, after which the worksheet assembly is placed in a forming die. The actual structure forming process begins by heating the die and its associated worksheet assembly to a temperature suitable for superplastic forming, and simultaneously applying gas pressure at the means for admission of pressurized gas.

Abstract: The structure and process for making a metallic panel structure from a plurality of core panels each comprised of a pair of sheets of superplastic material welded together along a plurality of weld lines. The core panels are joined together, with the weld lines of one core panel positioned normal to the weld lines of the adjacent core panel. The resulting assembly is placed in a die. The die is heated to superplastic forming temperature, and gas pressure is applied to the spaces between the sheets of the respective core panels, causing superplastic forming and expansion of the sheets of each core panel to form a series of bulges between weld lines of one core panel, and a series of similar bulges between weld lines of the adjacent core panel, the bulges expanding inwardly toward each other. The two series of bulges are orthogonally disposed, the bulges from the two core panels contacting and forming around each other.

Abstract: Process for fabricating a superplastically formed trusscore structure from a pair of core elements each formed of a pair of metal sheets of a superplastic material, e.g. titanium. The sheets of each core element are welded together along pairs of closely spaced weld lines, one core element having an even number and the other core element an odd number of such pairs of parallel weld lines. A slot is provided between the weld lines of each pair of weld lines. The two core elements are placed together, with the pairs of weld lines of one core element displaced laterally, preferably midway between the pairs of weld lines of the other core element. Face sheets are applied in contact with the outer sheet of each of the core elements, and the periphery of the assembly is sealed as by welding. The resulting forming pack asssembly is placed in the cavity of a forming die.

Abstract: An apparatus and method for controlling the superplastic forming process by measuring and controlling the gas mass flow rate of the gas displacing the blank being formed.

Abstract: Process for making a panel structure by superplastic forming from a pair of face sheets disposed on opposite sides of a core sheet, the core sheet being bonded as by welding to the face sheets along a plurality of spaced weld areas, the core sheet and face sheets having superplastic characteristics, which comprises placing a restraining sheet of superplastic material in contact with one of the face sheets and subjecting the forming pack of the face sheets and core sheet, together with the restraining sheet, to superplastic forming in a die while applying a back pressure against the restraining sheet. The back pressure is lower than the internal pressure and maintains the restraining sheet in contact with the adjacent face sheet while maintaining the other face sheet in contact with a surface of the die.